Secure communications systems and data storage systems have had great importance for military and diplomatic users for many years. These systems generally rely on physical security, where information is not accessible to unauthorized users in any form, and on encryption, where information is rendered illegible by application of some function before transmission or storage, and the function is reversed upon receipt or retrieval. Since a communications channel between two parties may often be tapped, as in the case of telephone, telegraph, and radio communications, encryption of such communications is particularly common where information being transmitted could be of high value to third parties. Similarly, information, whether data or computer programs, is often encrypted for storage to prevent access by unauthorized parties.
Secure communications are of importance outside the military and diplomatic corps also. In the banking industry, a malicious party who broke into the teller-machine networks, into the credit and debit card networks, or into bank account databases could conceivably access large sums of money. Similarly, it is desirable to keep medical records secure from those not involved in care of particular patients.
Many entities, including friendly and hostile governments, have invested heavily in cryptanalysis, the breaking into secure communications and data storage systems of other parties. Successful decryption of Japanese “Purple”, Japanese naval codes, and German Enigma cyphers by the Allies, and decryption of British merchant-marine codes by Germans all played an important part in World War II, just as decryption of the Zimmerman telegram played a part in dragging the United States into World War I. Hardware and software capable of breaking into many older, lower-security systems, like the “WEP” system commonly used for encrypting 802.11B/G wireless computer networks, is commonly available. Since computerized cryptanalysis technology is continually advancing, it is desirable to find better, more secure, yet faster, systems for encrypting and decrypting both communications and stored data.
Historical cipher systems often had two or more levels of security; for example the Naval version of the Enigma system used by Germany in World War II had a general level and an “officer-only” level. In that system, some high-security messages were enciphered first with an “officer-only” key, then an additional header was added and the message re-enciphered with a general-use key.